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The buckling length Lcr of a compression member is the length of an otherwise similar member with “pinned ends” (ends restrained against lateral movement but free to rotate in the plane of buckling) which has the same elastic critical buckling load.
In the absence of more accurate information, the theoretical buckling length for elastic critical buckling may conservatively be adopted.
An equivalent buckling length may be used to relate the critical load of a member subject to non-uniform loading to that of an otherwise similar member subject to uniform loading.
An equivalent buckling length may also be used to relate the critical load of a non-uniform member to that of a uniform member under similar conditions of loading and restraint.

Key words; effective length; 6.3.1.3

This NCCI sets out the basis for the calculation of alpha-cr, the parameter that measures the stability of the frame.

Keywords:frame stability;second-order effects; sway effects, imperfections, 5.2.1; 5.2.2

After a general discussion on connection classification, this document presents three approaches for determining values of column base stiffness for practical global analysis. The first, empirical, approach provides simple conservative ways of recognising that all practical column base arrangements have some rotational stiffness in practice. The second presents a more detailed analysis of the response of the column base steelwork. The third introduces a method for taking account of the interaction between the foundation and the surrounding soil

Keywords: modelling; baseplate; 5.1; 5.1.2, 5.1.3

For the following common cases, torsional and flexural torsional buckling will not give a lower mode than flexural buckling :
􀂉 Doubly symmetric I and H sections (provided that both flanges are restrained at positions of lateral restraint)
􀂉 Hollow sections
However, in some particular cases, the torsional buckling mode or the flexural-torsional buckling mode of an axially loaded member may correspond to a critical load lower than the one corresponding to the flexural buckling mode, especially for open sections. This document gives rules to determine the critical load for such cases.

key words:6.3.1.4; Ncrit; Ncr

This NCCI provides rules for determining either the design resistance or the required dimensions of base plates of simple columns, i.e. columns which are predominantly loaded in axial compression. While this NCCI is limited to covering symmetrical I section column bases, the rules given can be easily extended to bases of hollow section columns.

Key words; pinned base; baseplate

In trusses with structural hollow sections, the members are generally welded directly to each other. The selection of member sizes has a direct effect on the cost of fabrication and on the joint resistance. Therefore, it is important for the architect and the design engineer to recognise at the outset, the effects that their design decisions will have on the joint resistance, the fabrication, assembly and erection of the structure.

key words:truss; SHS; CHS; RHS; 7.2;7.4; 7.5; 7.6; 7.7

Bolted connections are usually convenient for site connections of prefabricated parts of the structure. RHS end plate splices have usually been bolted along the four sides of the plate, however, during the 1980s the possibility of bolting only on two opposite sides was investigated and it proved to be an effective solution. On the other hand, CHS splices usually present bolts evenly placed radially around the hollow section.
The recommendations for simple designs given in this NCCI have been taken from the relevant CIDECT Design Guides [1] [2]. Additional background on this topic may be found in an SCI/BCSA publication about joints in steel [3].

Key words: SHS; CHS; RHS

This NCCI provides the rules for the design of fixed column base joints. The rules are limited to covering the design of symmetric un-stiffened base plate joints of I section columns subjected to normal force, shear force and moment about the column major axis. The design of a shear nib, if required, is covered by NCCI SN021. The rules given can be easily extended to bases of other types of column sections.

key words: moment base; 6.2.8

Bracing is required to resist lateral loads, principally wind loads, and the destabilising effects of the imperfections defined in §5.3 of EN 1993-1-1. This bracing must be correctly positioned and have adequate strength and stiffness to justify the assumptions made in the analysis and member checks.
It is essential to provide bracing that is both sufficiently strong and sufficiently stiff at all the points that are assumed to be restrained in the design calculations. This is especially true where the inner flange of the portal frame is in compression. Consequently, this document can only give general guidance, not detailed advice. The design criteria given in EN 1993-1-1 are summarised within this document.

Key words; portals; 5.3; 5.3.3; 5.3.2

Bracing is required to resist lateral loads, principally wind loads, and the destabilising effects of the imperfections defined in §5.3 of EN 1993-1-1. This bracing must be correctly positioned and have adequate strength and stiffness to justify the assumptions made in the analysis and member checks.
It is essential to provide bracing that is both sufficiently strong and sufficiently stiff at all the points that are assumed to be restrained in the design calculations. This is especially true where the inner flange of the portal frame is in compression. Consequently, this document can only give general guidance, not detailed advice. The design criteria given in EN 1993-1-1 are summarised within this document.

Key words; portals; 5.3; 5.3.3; 5.3.2

This NCCI provides information on the design method for a bolted apex moment connection. It includes several simplifications which are explained throughout the document, to obtain simpler but conservative calculations. This NCCI references repeatedly to SN041 to benefit from the common approach to design apex and eaves connections and therefore only presents those contents specific for apex.

Key words:portal; moment connection; apex

This NCCI provides information on the design method for a bolted eaves moment connection. It includes several simplifications which are explained throughout the document, to obtain simpler but conservative calculations.

Key words: moment connection; haunch

The traditional analysis of a truss assumes that all loads are applied in the joints and that all joints in the truss are pinned. Even though this is generally not the case, since the upper and lower chords are normally continuous and the web members are often welded to the chords, it is still a common and acceptable procedure to determine the axial forces in the members. In a situation when the dimensions of the upper chord is very large and the overall depth of the truss is small the moments due to continuous upper chord has to be considered. However, this is rarely the case for roof trusses in industrial buildings that is treated here. Bending moments have to be considered in other cases, which will be explained here.

Key words: trusses

In many buildings, the structure and services zones beneath the floors are integrated, i.e. they share the same zone, in order to reduce the height between floors. In such integrated construction, various types of sizes of openings in the webs of the downstand beams are often provided. These openings may be in the form of regular circular openings in cellular beams or isolated rectangular openings in rolled or fabricated beams.
This NCCI presents three approaches to the design of beams with openings in the web, in ascending order of refinement and complexity.

Key words; arcelor; fabsec; westok; cellular

The method presented in this NCCI is applicable to steel framed buildings modelled as “simple” according to EN 1993-1-8 § 5.1.1 (2), in which the joints may be assumed not transmit any bending moment from the beams into the columns. The lateral stability of the frame must be provided by a system of bracing or by lift shafts and stair wells. Stability is not provided to any degree by the stiffness of the beam-to-column joints. The columns in this type of structure will primarily be loaded in axial compression, but “nominal” moments due to the eccentricity of the beam-to-column joints should also be considered in design.

Key words; columns; simple construction; nominal moments; 6.3.3

This NCCI presents a method for determining the non-dimensional slenderness without explicit determination of Mcr. The basic, conservative method can be refined to take account of section geometry and bending moment distribution.

key words: bending resistance; elastic critical buckling moment; Mcrit; Mcr; slenderness; 6.3.2

This NCCI gives guidance on the determination of the effective length of columns in truss and column construction. It also provides rules to calculate the effective length for chord and bracing members in truss and column construction.
In a welded lattice girder, chord and bracing members are partially fixed at the nodes, although the static calculation of the internal forces in the members is usually carried out assuming the joints to be pinned. As a consequence of this partial restraint, the value of the system length L may be reduced to obtain the effective buckling length Leff.
The rules given below are partly based on EN1993-1-1 Annex BB.1 (Buckling of components in building structures). Detailed information about the structural stability of hollow sections is given in CIDECT publications and the relevant information is summarized in section 3. Rules for special cases taken from DIN 18800 are presented within section 4.

Key words: critical buckling lenth; effective length

This NCCI gives the expression of the elastic critical moment for doubly symmetric cross-sections. Values of the factors involved in the calculation are given for common cases. For a beam under a uniformly distributed load with end moments or a concentrated load at mid-span with end moments, the values for the factors are given in graphs.

Keywords: Mcrit; lateral torsional buckling; 6.3.2.2; 6.3.2.3; C1 factor

This NCCI provides information for dealing with cantilever beams satisfying the following conditions: The beam has a uniform and doubly symmetrical cross-section The beam is unrestrained except at support The beam is torsionally restrained at support Loads are applied normal to the beam to cause bending about the major axis. The line of action passes through the shear centre (applied at, above or below the shear centre) Favourable effect of the in-plane deflection not accounted for (beam assumed straight in the plane of loading at buckling) Normal force negligible

Keywords: Mcrit;lateral torsional buckling; C1 factor; 6.3.2.2; 6.3.2.3

This NCCI clarifies the general method presented in §6.3.4 of EN1993-1-1 for verifying out-of-plane buckling of members in portal frames for which the methods given in §6.3.1 to §6.3.3 do not apply. The guidance is of particular relevance to non-uniform members or members with particular lateral restraint conditions.

Key words: portal; haunch; 6.3.4

This document provides design graphs for the selection of European rolled I-profiles to be used as secondary beams. These graphs give the maximum span length versus the slab span, for various profiles (IPE, HE) and various steel grades.
Two cases are considered :
􀂉 Lateral Torsional Buckling (LTB) is fully prevented
􀂉 No restraint to Lateral Torsional Buckling is provided, excepted at supports
Table 1.1 gives an overview of the design graphs available in this document. Where the figure number is replaced by a cross, this means that the deflection conditions govern the choice of section and a higher steel grade will not improve the loading capacity.

Key words: beam design, european sections; european profiles; 6.2.5; 6.2.6; 6.3.2

This document provides design graphs for the selection of Universal Beam profiles to be used as secondary beams (non composite beams). These graphs give the maximum span length versus the slab span, for various section ranges and steel grades. The lightest section is used for each range.

key words: Beam design; 6.2.5; 6.2.6; 6.3.2

This NCCI provides rules for the initial sizing of the components of fin plate connections for a "Simple joint". The rules apply to a bolted connection using non-preloaded bolts (i.e. a Category A: Bearing type bolted connection).

key words: fin plate; simple connection

This NCCI provides rules for the initial sizing of the components of fin plate connections for a "Simple joint". The rules apply to a bolted connection using non-preloaded bolts (i.e. a Category A: Bearing type bolted connection).

key words: fin plate; simple connection

In simple construction (see SN020), splices are generally provided just above floor levels, typically 500 mm (See SN025). The splice connections hold the connected columns in line along a common centroidal axis.
In non-bearing column splices, as described in SN025 and SN023, loads are transferred via bolts and cover plates. Any bearing between the ends of the columns is ignored and the splice is normally detailed with a physical gap between the two parts of the columns. The cover plates are generally arranged so that the centroidal axis of the splice material coincides with the centroidal axis of the column sections.
When joining columns of different serial size, multiple packs are necessary to take up the dimensional variations. In order to limit the packing thickness to reasonable proportion (about 30 mm) no more than one jump in the column serial size should be used at each splice.
Simplified guidance given in this document should only be used for initial sizing. Full verification (see SN023) will be necessary at the final design stage.

key words; splices

This NCCI provides rules for the initial sizing of the components of end plate connections for a "Simple Joint". Both partial depth and full depth end plates are covered by this NCCI. The rules apply to a bolted connection using non-preloaded bolts (i.e. Category A: Bearing type bolted connection).

key words: flexible end plate; simple connection; partial depth end plate;

The internal forces and moments in structures are usually calculated using a software programme. For common buildings, designers often prefer using, where relevant, 2D models whose data are easier to input and results are easier to deal with than 3D models. Portal frames can generally be calculated using a 2D model.

Keywords: portal frame; 5.1; 5.2; 5.2.1; 5.2.1(4)

This NCCI provides information for dealing with mono-symmetrical uniform members subjected to bending and axial compression satisfying the following conditions:
􀂉 The verification is restricted to the elastic behaviour of the member
􀂉 The cross-section is symmetrical about the weak axis
􀂉 The flanges and the web are made of the same steel grade
􀂉 The loads create bending moments about the strong axis only
􀂉 The axial load is expected to be applied at the centroid of the cross-section
􀂉 The web is made of a solid plate of constant thickness
􀂉 The effects of the fillet welds are not taken into account
Note 1: Such a mono-symmetrical cross-section is susceptible to torsional-flexural buckling |3|.
Note 2: This kind of cross-section can be found, for instance, in composite structures where the upper flange of the beam is connected to a composite slab by means of shear connectors. Then, the following calculations are required in the non-composite stage when the fresh concrete acts only as an external load. In this case, the smaller flange is generally mainly in compression.
This kind of cross-section can be found also in welded cross-sections when a higher resistance to torsional-flexural buckling is needed for the member. In this case, the smaller flange is generally mainly in tension.
Note 3: Cellular beams or beams made of two different hot-rolled profiles are not covered by this NCCI.

Key words: 6.3.3; combined;

Frame Stability (sensitivity to second-order effects) is covered in section 5.2 of BS EN 1993-1-1

This article in New Steel Construction offers an overview of the Eurocode provisions

Design of steel to BS EN 1993 need not be complex - and the physics has not changed since BS 449.

This article in New Steel Construction suggests how design to the Eurocode may be made simple

Web bearing and buckling checks are described as "local buckling effects in clause 6.2.1(2). The actual checks are found in 1993-1-5, rather than 1993-1-1.

This article in New Steel Construction describes the checks, and how the resistances are tabulated in the Blue Book

Web bearing and buckling checks are described as "local buckling effects in clause 6.2.1(2). The actual checks are found in 1993-1-5, rather than 1993-1-1.

This article in New Steel Construction describes the checks, and how the resistances are tabulated in the Blue Book

Clause 6.3.1.4 describes torsional and torsional-flexural buckling. In some circumstances, these are the critical modes of buckling, for example for cruciform sections, or asymmetric sections with different restraints to each flange.

This article in New Steel Construction describes the phenomena, and gives background to the checks

Resistance tables are available in the Blue Book. The publication covers S275 and S355 steel, and provides section properties, effective section properties, including compression, bending, tension, combined axial load and bending, web bearing and buckling, bolt and weld resistances.

This article in New Steel Construction describes the buckling tables

Portal frames verified by plastic design are commonly fabricated from hot-rolled I-sections. It is generally most economic to have haunches to deepen the rafters at the columns as shown in Figure 1.1 below. It is essential that the section classification is Class 1 at all plastic hinge positions and so it is most common to use Class 1 sections throughout the columns and rafters. It is common to use Class 3 webs and Class 1 flanges for the haunches, provided that in the Class 3 portion of the web either the stress distribution remains elastic or the requirements of EN 1993-1-1 §6.2.2.4 are satisfied and no plastic hinge occurs.

key words: haunch; portal design; 5.2.1;5.2.2

No specific deflection limits are set in Eurocode 1993-1-1 [1]. According to EN 1993-1-1, § 7.2 and EN 1990 – Annex A1.4 [2], deflection limits should be specified for each project and agreed with the client. The National Annex to EN 1993-1-1 may specify limits for application in individual countries. Where limits are specified they have to be satisfied. Where limits are not specified, the following might be helpful when deciding relevant deflection limits.

Keywords: portal frame; eaves deflection

This NCCI provides rules for the determination of shear resistance of a "Simple Joint" using an end plate connection for Beam/Column and Beam/Beam connections. This NCCI covers the rules for the end plate, the supported beam and the supporting column or beam. The rules may be used to evaluate the overall shear resistance of the connection, for all the possible modes of failure, based on the rules in EN 1993-1-8 for determining the resistances of individual components of the connection. The rules apply to a bolted connection using non-preloaded bolts (i.e. a Category A: Bearing type bolted connection). The rules given in this NCCI can be applied to both partial depth and full depth end plate connections.

Keywords; flexible end plate; pinned connection; 6.1.3; 3.6; 3.6.1; Table 3.4

All structures contain imperfections and for steel structures EN 1993-1-1 § 5.3 explicitly defines the allowances in structural analysis to cover their effects.
The treatment of imperfections in EN1993-1-1 is very general, in order to be applicable to all forms of steel construction.
This NCCI provides a simplified approach to these effects that focuses on the appropriate treatment of imperfections for low and medium-rise multi-storey buildings. It proposes horizontal force coefficients that are simple to apply and will be familiar to experienced users of previous national design standards.

Key words: sway; imperfections; frame stability; braced frames; 5.3; 5.3.1; 5.3.2; 5.3.3

This NCCI provides design graphs for the selection of Euronorm H-profiles to be used as columns in simple construction. The document may be used to make an initial selection of column sizes for internal and external columns over the full height of a building. The selection is based on estimated axial forces in the columns, the storey height and the chosen steel grade (S235, S275 or S355).

Key words: european profiles

The document may be used to make an initial selection of column sizes for internal and external columns over the full height of a building. The selection is based on estimated axial forces in the columns, the storey height and the chosen steel grade (S235, S275 or S355).

Keywords; multi-storey; 6.3; 6.3.1; 6.3.1.3; 6.3; Annex B

This NCCI provides guidance about the verification of a member subject to torsion.
When a member is loaded by transverse forces whose resultant does not pass through the shear centre of the cross-section, the member is subject to stresses due to torsion. These stresses should be combined with those due to bending and shear forces.
This NCCI gives some guidance for the verification of a member in torsion. It contains the equations to calculate the stresses due to torsion, and expressions for the calculation of the torsional properties concerning common profiles. References are given for more complex cases.
This document deals with uniform members only.

Key words; 6.2.3; 6.2.7,

This NCCI provides rules for the determination of tying resistance of a “Simple Joint” using an end plate connection for beam-to-column and beam-to-beam connections. It covers the rules for the end plate, the supported beam and the supporting column web. The rules may be used to evaluate the overall tying resistance of the connection, for all the possible modes of failure, based on the rules in EN 1993-1-8 for determining the resistances of individual components of the connection. The design procedure given in this NCCI applies to an accidental limit state. The rules given in this NCCI can be applied to both partial depth and full depth end plate connections, using non-preloaded bolts (i.e. Category A: Bearing type bolted connections).

Key words: robustness; tying; flexible end plate; partial depth end plate; 2.1.3.1; 1991-1-7

This NCCI proposes a new expression for the verification of columns that will avoid the calculation of “k” factors in Annexes A and B of EN 1993-1-1.

For the design of columns in the following situations:
The column is a hot rolled I or H section, or rectangular hollow section,

• The cross section is class 1, 2 or 3 under compression,
• The bending moment diagrams about each axis are linear,
• The column is restrained laterally in both the y and z directions at each floor but is unrestrained between floors.

Relates to: Simple Connections

Keywords: Eccentricity

No specific deflection limits are set in EN 1993-1-1 [1]. Instead it states in § 7.2 that the serviceability criteria, including deflection limits, should be specified and agreed with the client for each project. Furthermore, the verification should be based on criteria concerning deformations that affect appearance, comfort of users, functioning of the structure or that cause damage to finishes or non-structural members. In some countries, the National Annex to EN 1993-1-1 specifies the limits. Where limits are specified they have to be observed.

Key words; SLS; deflection; 7.2; 7.2.1; 7.2.2